Variable resistor construction



May 3, 1960 M- E BOURNS 2,935,716

VARIABLE RESISTOR CONSTRUCTION original Filed May 5, 1954 INVENTOR MARLAN E. BOURNS United States Patent 2,935,716 VARIABLE RESISTOR CONSTRUCTION Marlan E. Bourns, Riverside, Calif.

3 Claims. (ci. ass- 180) The present invention relates to new and improved variable resistor constructions, and is a continuation of mypending application, Serial No. 427,326, filed May 3, 1954, now Patent No. 2,831,949, granted April 22, 1958, entitled Variable Resistor Constructions. 1

One of the primary objects of the present invention is toprovide a new and improved variable resistor of the leadscrew actuated typ'e, which is extremely'V` compact, reliable, and simple in construction.

Another object of the invention is to provide a variable resistor of the class described which is inexpensive to manufacture and, in particular, one in which the leadscrew is quickly and easily assembled with the body.

Still a further object of the invention isto provide a variable resistor having novel means for securingy the leadscrew against endwise movement with respect to the body.

The foregoing and other objects and advantages of the present invention will become apparent to those skilled in the art, upon consideraiton of the following detaied description, together with the accompanying drawings, wherein:

Figure 1 is a side elevational view of a variable resistor embodying thev principles of the invention;

Figure 2 is a cross sectional view of the same, taken 2--2 of Figure l;

Figure 3 is a cross sectional view, taken at 3-3 of Figure 2;

Figure 4 is a fragmentarysectional view, taken at line 4-4 of Figure 2;

Figure 5 is another fragmentary sectional view, taken at 5-5 of Figure 2;

Figure 6 is a perspective viewofa slider employed in the construction of Figure 1; Y

Figure 7 is a perspective view of a contact which is carried by the slider shown in Figure 6;

Figure 8 is a cross sectional view similar to Figure 3, showing a modified form of the invention;

Figure 9 is a similar cross sectional view of still another form of the invention; 1

Figure 10 is a sectional vieu/,takenat'lO-JIO ofFig-v ure9;and`

Figure 11 is a fragmentary sectional View, showing the manner of connecting one of the terminal lugs to the resistance element.

First to be described will be the embodiment shown in Figures l to 7, inclusive, of the drawings. The variable resistor is designated n its entirety by the reference numeral 10, and comprises a body 11 of nonconductive material such as plastic, ceramic, or the like, having a channel-shaped lid or cover 2d Wrapped around three sides thereof. The body 11 is provided with a substantially flat upper surface 12 and upstanding ends 14. The sides 15 of the body are recessed at 16 and 17 to receive the side walls 19 ofthe U-shaped cover 20. The top section 21 of the cover 20 is disposed generally parallel to the flat upper surface 12 between the ends 14 of the body member 11, and overlies the ends 14, to which it atA member ICC . 2 is secured by means of tabs 22 that extend down over the ends of the body within notches 23. At the bottom side of the body, the tabs 22 are turned under, as shown at 26, and are seated within cavities 25.

The upper surface 12 of the'body 11 is provided with a longitudinally extending channel 30, in which is seated Y an inverted, U-shaped conductor 31 that serves as an electrical return means from the resistance element. Projecting downwardly from one side of the conductor 31 is a terminal tab 32, which passes through an opening 33 in the bottom of the body 11.

Parallel to the channel 30 is another channel 34, which holds a resistance element 36. The element 36 consists of resistance wre wrapped around a nonconductive card or mandrel 35, and the element is normally held in place by means of terminal tabs 37 projecting through apertures 38 in the bottom of the bodyli. The tabs 37 are preferably bowed slightly, as shown at 39 in Figure 2, so that they are held within the apertures 38 by spring tension.

Disposed between the cover 20 and the body 11 is a slider, or carrier 40, having a U-shaped contact member 44 on the under side thereof which wipes on both the conductor 31 and resistance element 36. In the embodiment illustrated in Figures l to 7, the carrier 40 cornprises a generally rectangular shaped block of non-conductive plastic, and is provided with an internally threaded bore 41 throughwhichr a leadscrew 50 passes. Also formed in the sides of the slider 40 are narrow, verticaly slots 42 which receive upwardly projecting ears 43 of the contact member 44. The contact member 44 includes spring fingers 45, which wipe on the conductor 31 and element 36.

The leadscrew 50 is in the'form of an elongated shaft having a threaded center section 51 and smooth ends 52 and 53. The end 52 is rotatably supportedwithin a cavity 54 in the left-hand end 14 of the body; while the other end 53 is seated within a notch 56 in the righthand end 14 and projects beyond the end of the body. End 53 of the shaft is held against endwise movement by aninwardly projecting flange 57 in the notch 56, and by means of a similar projection 58 (see Figure 4) extending downwardly from the top 21 of the cover 20. Projections 57 and 58 engage a shoulder, which may conveniently be provided by a circumferential groove 55 in the shaft 50. Y

At the other end of the shaft 50, a projection 59 'exrtends downwardly from the top 21 of the cover and bears aganist the smooth portion 52, as best shown in Figure 5. Both of the projections 58 and 59 exert a slight pressure on the shaft so as to provide a certain amount of frictionaleresistance to rotation. With this arrangement, the slider 40 and contact member 44 are moved lengthwise of the resistance element 36 and conductor 31 by rotating the leadscrew in one direction or the other. The slider'40 is prevented from turning with the shaft 50 by means of runners, or lugs 63, which project downwardly from the under side of the slider 40 and slidably engage the exposed sides of the conductor 31.

The modified construction shown in Figure 8 of the drawings differs from that shown in Figures l through 5 in that the conductor and resistance element are in the formrof a ymetal strip 64 and a strip 60 of resistive cornposition material or the like, both of which are disposed within parallel grooves 61 in the body member 11. Another difference in the construction of Figure 8 is that the terminal tabs 62 are wedged within apertures 63 in the body 11, and include bent-over spring contact portlons that overlie the conductor 64 and element 60, and make electrical contact with the top surfaces thereof. With this specific construction,y the tab employed with the conductor strip 64 is located adjacent to one end 3 thereof, so as not to interfere with the movement of the contact 44.

Another form of the invention is shown in Figures 9 and 10, which particularly illustrates a yieldable driving connection between the leadscrew and the slider 40.` In this form of the invention, terminal tabs 65 aremolded within the body 11 so as to project above the top surface 12, and are bent over at right angles to overlie resistance films 66, which are positioned upon supporting bases 67 of nonconductive material seated within slots Y58. The tabs 65 may be soldered, as shown at 69, to the resistance film.

The slider 4t) employed with the modified construction shown in Figures 9 and l0 differs from those previously described, in that the bore i1 is somewhat oversize and is not threaded. Extending down intothe slider' di) from the top side thereof is a cavity 71, which ex tends below and intersects the bore 41.

Seated within the cavity 71 is a V-shaped spring clip 72 having sides 73 and 74 that are joined at an apex 75. Both of the sides 73, 74 are provided with holes 76 and 77, respectively, which are of such a dimension that when the sides 73, 74 are bent together, the shaft 50 passes freely through the holes without having to screw the shaft through the holes, as is necessary with a threaded hole, such as in the embodiment of Figure 2. When the slider has been moved to the desired location along the length of the leadscrew, the sides 73, 74 are released, allowing them to spring outwardly. As the sides 73, 74 spread apart, the top and bottom edges of the hol 76, 77 grip the leadscrew on opposite sides thereof, and at least one et' the said edges drops down into the thread of the screw portion Si to provide a driving connection between the leadscrew and the slider. At the Sametime, the sides 73, 74 engage the edges 78 of the cavity 71 so as to wedge the spring clip 72 against the slider40 in such a manner that as the shaft Si) isturned, the slider 4h is moved one way or the other along the length of the resistance clement.

One advantage of the above-described arrangement is that it substantially eliminates backlash, ysince the thread of the leadscrew is resiliently gripped by the spring clip. Another advantage is that the sides 73, 74 of the spring clip are capable of yielding under excessive force, and ride up over the threads of the leadscrew. Thus, if the slider 40 is moved to the end of its travel in either direction and is abutting against the body, it is impossible to damage either the body or the slider by forcibly turning the leadscrew.

Both of the sides 73, 74 terminate in bent-over end sections 79, which slidably engage the under side of thev top section 21 of cover 2i) to prevent the slider 40 from rotating when the shaft 50 is turned. The end sections` 79 press against the cover 20 with a yielding spring pressure of suiicient force to resist the torque exerted on the spring clip 72 by the leadscrew.

While I have shown and described certain illustrative forms of the invention in considerableV detail, it will be understood that various changes may be made in the shape and arrangement ,of the several parts without departing from the scope of the following claims.

I claim:

1. A device of the class described, comprising a base member having a mounting surface and upturned end portions at opposite ends thereof, said upturned end portions having axially aligned notches provided therein, a resistance element mounted on said surface, a cover positioned over said base member and spaced generally from `said surface, a slider disposed between said cover and said mounting surface, spring contact means carried by said slider and engaging said resistance element, a

rotatable shaft having bearing portions seated within said notches having a projection provided therein which seats in said circumferential groove to prevent endwise move# ment of said shaft, .and said cover having projections engaging said shaft to hold the same down into said notches.

2. A variable resistor comprising a housing having two members, at least one of said members having a partial wall at the end of said cavity, said wall having a notch provided therein, a rotatable leadscrew disposed within said notch, passing within said cavity and projecting through one end of said housing, shoulder means on said leadscrew adjacent one end thereof, and cooperating means on said housing engaging said shoulder means to' prevent endwise movement of said leadscrew, said other housing memberengaging said shaft to confine the same" in place within said notch, an electrical element mounted within said cavity, a carrier mounted on said leadscrew, said carrier having a contact which rides on said resistance element, and electricalreturn means electrically connected to said contact.

3. A housing for a variable resistor including a re sistance element, a slide engageable with said element, and a screw shaft for moving said slide, said screw shaft having an annular shoulder near one end, said housing comprising: a base member channel-shaped in lengthwise aspect to form upturned ends having axially aligned grooves in their upper ends to journal said screw shaft, one of said grooves having shoulder-engaging means to restrain said screw shaft against axial displacement; and a cover member channel-shaped in transverse aspect forming a web for covering said base member between said ends and side walls enclosing the sides of said body member between said upturned ends, said cover member including bearing means complementary to said bearing grooves to retain said screw shaft therein.

References Cited in the tile of this patent UNITED STATES PATENTS 1,225,227 Dunham May 8, 1917 1,687,628 Martin Oct. 16, 1928 2,439,069 Anderson Apr. 6, 1948v 

